This invention relates to a nonradiative dielectric waveguide used in a high frequency band of, e.g., millimeter-waves and a millimeter wave transmitting/receiving apparatus using such a nonradiative dielectric waveguide.
A first construction example of a conventional nonradiative dielectric waveguide is described with reference to FIG. 34. In the following, the nonradiative dielectric waveguide is referred to as an NRD guide. The NRD guide shown in FIG. 34 is constructed by providing a dielectric strip 703 between a pair of parallel plate conductors 701, 702 whose spacing is xcex/2 or shorter when a wavelength of an electromagnetic wave (high-frequency wave) propagating in the air at an operating frequency is xcex, and is based on such an operation principle that the electromagnetic wave transmits along the dielectric strip 703, and radiation of the transmitting wave is suppressed by the blocking effect of the parallel plate conductors 701, 702. In FIG. 34, the upper parallel plate conductor 701 is partly cut away so as to make the inside visible.
The NRD guide according to the first conventional construction example may include a curved dielectric strip 704 between the pair of parallel plate conductors 701 and 702. Such a construction enables an electromagnetic wave to easily be transmitted in a curved manner and has advantages of miniaturization of a millimeter wave integrated circuit and a circuit design with a higher degree of freedom. In FIG. 35, the upper parallel plate conductor 702 is shown in broken line so as to make the inside visible.
There are known two modes, i.e., an LSM (longitudinal section magnetic) mode and an LSE (longitudinal section electric) mode as millimeter wave transmission mode of the NRD guides. The LSM mode having a smaller loss is generally used. Since the parallel plate conductors 701, 702 of the conventional NRD guides need to have a high electric conductivity and an excellent processability, conductor plates formed of Cu, Al, Fe, SUS (stainless steel), Ag, Au, Pt or like metallic material have been used. Alternatively, insulating plates made of ceramics or resin having a conductive layer made of the above metallic material formed on the outer surface have also been used.
Teflon (trademark of polytetrafluoroethylene), polystyrene and like resin material having a relative dielectric constant of 2 to 4 have been used for the dielectric strips 703, 704 due to their good processability. The dielectric strips 703, 704 have been secured to the parallel plate conductors 701, 702 by an adhesive.
However, if the NRD guide is constructed by the dielectric strip formed of the conventionally used Teflon, polystyrene or dielectric material having a relative dielectric constant of 2 to 4 in the first conventional construction example, there is a problem that a steeply curved portion cannot be provided because of a bend loss and a large transmission loss at a joining portion of the dielectric strip. Even if a moderately curved portion could be provided, a radius of curvature of the curved portion would need to be precisely determined. However, there is a restriction in precisely setting the radius of curvature if the dielectric strip is made of Teflon, polystyrene or like material.
Further, a bend loss at the curved portion can be suppressed to a practically negligible level by strictly specifying a curvature of the dielectric strip in conformity with the operating frequency. However, the bend loss increases upon even a slight shift of the operating frequency. For instance, if an attempt is made to reduce a bend loss at and near 60 GHz, a width of its permissible range is only about 1 to 2 GHz. This is because, in the case that the NRD guide is formed using a dielectric material having a relative dielectric constant of 2 to 4, part of the millimeter wave of the LSM mode is converted at a curved portion thereof into that of the LSE mode to increase a loss because distribution curves of the LSM mode and the LSE mode are very approximate to each other.
In the case that a high-frequency device, a high-frequency circuit module or the like is fabricated using the NRD guide having the dielectric strips 703, 704 made of an inorganic compound such as ceramics, it is possible to provide a steeply curved portion at the dielectric strips 703, 704, but not possible to provide a high bending dimensional precision. Thus, it has been difficult to fabricate such a complicated configuration comprised of a plurality of linear and curved portions. There is an additional problem of breaking or damaging the dielectric strips 703, 704 due to a difference in thermal expansion coefficient between the parallel plate conductors 701, 702 and the dielectric strips 703, 704, an impact, and other factors.
Further, it has been difficult to suppress a transmission loss of a high-frequency signal to or below a specified value in any of the NRD guides according the first conventional construction.
Next, a second construction example of the conventional NRD guide is described. The NRD guide of the second construction example is constructed, as disclosed in Japanese Unexamined Patent Publication No. 8-65015, such that a dielectric strip is provided between a pair of parallel plate conductors, two small projections are formed on the dielectric strip, and recesses engageable with the small projections are formed in one of the parallel plate conductors. In the thus constructed NRD guide, the parallel plate conductors and the dielectric strip can be precisely positioned with respect to each other by fitting the small projections into the recesses.
Other construction examples in which the parallel plate conductors and the dielectric strip are precisely positioned with respect to each other include those disclosed in Japanese Unexamined Patent Publication Nos. 6-260824 and 9-64608. Specifically, these publications disclose that a dielectric member is made of a strip section and collars formed on the upper and lower surfaces of the strip section to prevent a displacement of the strip section, and parallel plate conductors are formed by applying plating of, e.g., copper, silver or a silver paste to the upper and lower surfaces of the dielectric member and baking it.
In the NRD guides of this type, resin materials having a relative dielectric constant of 2 to 4 such as Teflon and polystyrene as mentioned above and ceramic materials such as alumina and cordierite are frequently used as the material of the dielectric strips. Since the dielectric strips need to be precisely positioned, the dielectric strips and the parallel plate conductors are adhered by using an epoxy resin or an organic adhesive having a high heat resistance such as a polyimide resin or a BT resin as disclosed in Japanese Unexamined Patent Publication No. 10-163712. In the case that positioning is not sufficiently precise by the above adhesion, the construction disclosed in Japanese Unexamined Patent Publication No. 8-65015 is adopted.
In the second conventional construction example in which the small projections of the dielectric strip are fitted into the recesses of the parallel plate conductor, it is impossible to arrange the dielectric strip unless the positions of the small projections and the recesses agree. Even if the positions of the small projections and the recesses agree, it is difficult to precisely position the dielectric strip if the small projections are too small or the recesses are too large. This disadvantageously increases a transmission loss of a signal in a coupler formed by bringing connecting portions with the respective devices such as diodes, circulators, terminators closer to the dielectric strip.
In the NRD guide in which the dielectric member is comprised of the strip section and the collar portions, it is difficult to process the same with a good dimensional precision, and a separate housing or the like needs to be provided since the parallel plate conductors formed by baking the plating or silver paste have a low strength. The NRD guides in which the adhesive made of an epoxy resin is used have a low reliability when being used in a severe environment because the epoxy resin has a low heat resistance, whereas those in which the adhesive made of a polyimide resin or BT resin is used have a problem of deterioration with time when being exposed to a severe environment.
It has been also difficult to suppress a transmission loss of a high-frequency signal to or below a specified value in any of the NRD guides according the second conventional construction.
Next, a third construction example of the conventional NRD guide is described. The NRD guide of the third construction example is constructed such that a mode suppressor is provided at an end of a dielectric strip provided between a pair of parallel plate conductors by providing a conductive layer inside the dielectric strip. More specifically, an operation mode of the NRD guide is generally an LSM mode. However, the NRD guide is sometimes connected with a circulator, an oscillator or like device in designing a circuit, and an LSE mode occurs at a connecting portion with the circulator, the oscillator or the like device. An LSE mode suppressor is provided between the NRD guide and the other circuit device in order to suppress the transmission of the LSE mode.
In such NRD guides, resin materials having a relative dielectric constant of 2 to 4 such as Teflon and polystyrene are frequently used as the material of the dielectric strips. Known mode suppressors are formed by splitting the dielectric strip into two half pieces, printing a conductive layer of a specified shape on one surface of one half piece, and placing the other piece next to a conductive layer surface of the one half piece where the conductive layer is formed, or securing the conductive layer surface of the one half piece to the other half piece by an adhesive.
Japanese Unexamined Patent Publication No. 63-185101 discloses a mode suppressor obtained by forming a metal plate of a specified shape and integrally molding this metal plate and a dielectric strip made of a polystyrene or like material.
However, in the third conventional construction example, an uncontrollable clearance is formed between the two half pieces of the dielectric strip during production if the two half pieces are arranged side by side and an operating band of the mode suppressor is shifted due to the presence of an area having a different dielectric constant between the two half pieces even if the two pieces are secured by the adhesive. The mode suppressor cannot effectively function in the case of deviating from a frequency band suppressable by the mode suppressor. Further, if, for example, the circulator and the metal plate are displaced from each other due to the displacement of the two half pieces of the dielectric strip, the operating band of the circulator is changed, with the result that the circulator may not properly function.
Further, in the NRD guide disclosed in Japanese Unexamined Patent Publication No. 63-185101 in which the metal plate of a specified shape and the dielectric strip made of, e.g., polystyrene are integrally formed, it is difficult to control a position where the metal plate is formed. If the position of the metal plate is displaced, the function as a mode suppressor is impaired. Further, if the width of the dielectric strip is narrow, it becomes difficult to handle the metal plate, making it impossible to precisely provide the metal plate in a specified position.
If the dielectric strip is made of Teflon, the position of the dielectric strip may be undesirably displaced while being handled since it is difficult to secure Teflon by an adhesive.
It has been also difficult to suppress a transmission loss of a high-frequency signal to or below a specified value in any of the NRD guides according the third conventional construction.
Next, a fourth construction example of the conventional NRD guide is described. Similar to the third conventional construction example, the NRD guide of the fourth construction example is constructed such that a mode suppressor is integrally provided by arranging a conductive layer inside the dielectric strip. Similar to the one shown in FIG. 34, a conventional NRD guide for transmitting high-frequency signals of a microwave and a millimeter wave is constructed by providing a dielectric strip having quadrilateral, e.g., rectangular cross section between a pair of parallel plate conductors opposed to each other at a specified spacing. By setting the spacing between the parallel plate conductors at xcex/2 or shorter when a wavelength of a high-frequency signal is xcex, the high-frequency signal can be transmitted by the dielectric strip while eliminating entrance of noise into the dielectric strip from the outside and radiation of the high-frequency signal to the outside. As described above, the wavelength xcex is a wavelength in the air (free space) at an operating frequency.
The operation mode of the high-frequency signal (electromagnetic wave) transmitting in the dielectric strip of such an NRD guide is the LSM mode as described above. However, the unnecessary LSE mode occurs at a circulator, a high-frequency oscillating portion and the like which are assembled into the NRD guide. A mode suppressor is provided at an end of the dielectric strip in order to effectively suppress this LSE mode by attenuation.
This conventional mode suppressor is shown in FIGS. 36 and 37. In FIGS. 36 and 37, identified by 705, 706 are parallel plate conductors which are parallelly arranged at a spacing of half the wavelength of a high-frequency signal, by 707 a dielectric strip made of Teflon, polystyrene or like material, and by 708 a mode suppressor provided at the leading end of the dielectric strip 707. The mode suppressor 708 is formed by arranging a strip conductor 709 in the leading end of the dielectric strip 707 for blocking a millimeter wave signal of the LSE mode whose electric field is parallel to a transmission direction of the high-frequency direction in the dielectric strip 707 and also to a plane perpendicular to the principle planes of the parallel plate conductors 705, 706.
Specifically, the mode suppressor 708 is formed by arranging a conductive layer of Cu, Au, Ag or like material along a direction perpendicular to the principle planes of the parallel plate conductors 705, 706 and along a signal transmission direction at a widthwise center position of the dielectric strip 707. In order to eliminate a TEM mode into which the LSE mode is converted at this conductive layer, wide portions (width W1) and narrow portions (width W2) are alternately formed at intervals of L which is xc2xc of the wavelength xcex of the electromagnetic wave of the TEM mode, i.e., a so-called xcex/4 choke pattern is formed (see Japanese Unexamined Patent Publication No. 63-185101).
There has been also proposed another conventional NRD guide in which conductive pins whose dimension along the signal transmission direction is xc2xc or shorter than the wavelength between the dielectric strips of a transmission mode are arranged at an interval which is xc2xc or shorter than the wavelength between the dielectric strips of the transmission mode in such a manner as to extend in a direction perpendicular to the upper and lower conductive plates in the dielectric strip at a widthwise center position of the dielectric strip, thereby enabling low-cost production of precise NRD guides having a uniformed variation of production characteristics (Japanese Unexamined Patent Publication No. 9-219608).
However, in the fourth conventional construction example having the mode suppressor disclosed in Japanese Unexamined Patent publication No. 63-185101, the TEM mode can be effectively suppressed, but there are cases where the entire more suppressor experiences resonance with unnecessary modes other than the TEM mode, undesirably resulting in insufficient attenuation of the LSE mode and like modes.
Further, since the mode suppressor disclosed in Japanese Unexamined Patent Publication No. 9-219608 is considerably thick: about 1/3 of the width of a block used as the dielectric strip, reflection of the LSM mode which is a transmission mode occurs, with result that a transmission loss is likely to increase.
It has been also difficult to suppress a transmission loss of a high-frequency signal to or below a specified value in any of the NRD guides according the fourth conventional construction.
Next, a fifth construction example of the conventional NRD guide is described. A circulator is incorporated into the NRD guides according to the fifth conventional construction example. A basic construction of the NRD guide incorporating the circulator is, similar to the one shown in FIG. 34, such that a dielectric strip having quadrilateral, e.g., rectangular cross section is arranged between a pair of parallel plate conductors opposed to each other at a specified spacing. By setting the spacing between the parallel plate conductors at xcex/2 or shorter when a wavelength of a high-frequency signal is A, the high-frequency signal can be transmitted by the dielectric strip while eliminating entrance of noise into the dielectric strip from the outside and radiation of the high-frequency signal to the outside. As described above, the wavelength xcex is a wavelength in the air (free space) at an operating frequency.
The conventional circulator incorporated into such an NRD guide is shown in FIG. 38. In FIG. 38, identified by 710, 711, 712 are dielectric strips made of Teflon, polystyrene or like material, by 713, 714, 715 mode suppressors provided at the leading ends of the respective dielectric strips 710, 711, 712 and formed by providing strip conductors 716, 717, 718 made of a copper foil in the dielectric strips 710, 711, 712 for blocking electromagnetic waves of the LSE mode, and by 719, 720 two ferrite disks which act as a circulator and are connected with the leading ends of the respective mode suppressors 713, 714, 715 and from which the dielectric strips 710, 711, 712 radially extend at an interval of 120xc2x0. The strip conductors 716, 717, 718 are formed in a xcex/4 choke pattern in order to eliminate the TEM (transverse electromagnetic) mode (see xe2x80x9cMillimeter Wave Integrated Circuit Using a NRD guide (By Yoneyama)xe2x80x9d, pp.87-94 of xe2x80x9cElectronic Information Communication Meeting Conference Papersxe2x80x9d C-I Vol.J73-C-1 No. 3, March 1990).
In such a construction, the electromagnetic wave having transmitted in the dielectric strip 710 has its wavefront rotated counterclockwise by the ferrite disks 719, 720 and is transmitted to the dielectric strip 711, but is not transmitted to the dielectric strip 712. Likewise, the electromagnetic wave having transmitted in the dielectric strip 711 is transmitted to the dielectric strip 712. In this way, transmission paths of the electromagnetic waves are changed.
In an NRD guide provided with the circulator and the dielectric strips, stepped portions 732, 733, 734 having a height equal to the thickness of the ferrite disks 730, 731 are formed in the upper and lower surfaces at the leading ends of mode suppressors 724, 725, 726, and the two ferrite disks 730, 731 are supported by the mode suppressors 724, 725, 726 by engaging the ferrite disks 730, 731 with the upper and lower stepped portions 732, 733, 734 as shown in FIG. 39, thereby ensuring the concentricity of the ferrite disks 730, 731 with a better repeatability and a higher precision (see Japanese Unexamined Patent Publication No. 9-186507). In FIG. 39, identified by 721, 722, 723 are dielectric strips, and by 727, 728, 729 strip conductors made of a copper foil or the like for constructing the mode suppressors 724, 725, 726.
In the fifth conventional construction example, the circulator for the NRD guide is mainly constructed by the two ferrite disks 719, 720 concentrically arranged while being vertically spaced from each other at a specified distance. In the construction shown in FIG. 38, a cylindrical dielectric spacer 760 for arranging the two ferrite disks at a specified spacing is necessary. In the conventional circulator using the dielectric spacer 760, a pass frequency band is narrowed and frequency varies as a relative dielectric constant changes due to the thickness of the cylindrical dielectric spacer 760. As a result, a center frequency of the pass frequency band has been undesirably shifted.
On the other hand, in the construction shown in FIG. 39, assembling repeatability of the circulator is improved and the upper and lower ferrite disks 730, 731 are free from eccentricity since the stepped portions 732, 733, 734 are formed at the leading ends of the mode suppressors 724, 725, 726. Thus, band characteristics of positive pass frequencies between ports of the respective dielectric strips are equal to each other and take a trapezoidal form symmetrical with respect to a center frequency of the pass band. As a result, flat pass band characteristic and isolation characteristics symmetrical with respect to the center frequency can be obtained.
However, besides the flat pass band characteristic, essential characteristics required for the circulator include the one for reducing reflection of the high-frequency signal at the circulator portion by reducing the transmission loss (insertion loss). This characteristic is not referred to by the prior art.
As a construction for improving a transmission loss, there has been proposed the one in which the leading end of a mode suppressor of a dielectric strip is cut off to form a step and a step-shaped impedance converter is provided, thereby improving an insertion loss and an isolation (see Singakugiho MW83-135, pp 63-66 (by Yoneyama, Sugatani, Nishida), 1984). However, in this proposed construction, a band width of an insertion loss of 1 dB in a band of 50 GHz is about 1.5 GHz, isolation is a minimum of 24 dB and a maximum of 30 dB in this band. The width of the band where the insertion loss and the isolation are improved is narrow and, therefore, effects of the improvement are insufficient. Further, it is difficult to finely process the dielectric strip to narrow its width stepwise, thereby standing as a hindrance to mass-productivity.
It has been also difficult to suppress a transmission loss of a high-frequency signal to or below a specified value in any of the NRD guides according the fifth conventional construction.
Next, a sixth construction example of the conventional NRD guide is described. In the NRD guide according to the sixth conventional construction example, a waveguide is connected with a dielectric strip. As described above, the use of the NRD guide constructed by tightly holding the dielectric strip by the pair of parallel plate conductors as one type of the transmission strip of the high-frequency signal is known. In the case that this NRD guide is assembled on a circuit board, it is essential in designing a circuit to connect it with an other transmission strip for a high-frequency signal, an antenna or the like. In such a case, it is important to connect them without deteriorating transmission characteristics.
As a construction for connecting the NRD guide with an other high-frequency transmission strip, a construction for connecting it with a micro-strip has been proposed. A general construction thereof is shown in FIG. 40. In the construction shown in FIG. 40, a dielectric strip 743 is arranged between a pair of parallel plate conductors in an NRD guide. A slot 744 is formed in one parallel plate conductor 741, and the NRD guide and a micro-strip are electromagnetically connected via the slot 744 by placing a dielectric substrate 746 having a center conductor 745 formed on its outer surface on the parallel plate conductor 741 such that the slot 744 and a rear end of the center conductor 745 have a specified positional relationship.
Although unillustrated, there is also known, as a construction for connecting a dielectric strip of an NRD guide and a waveguide, a construction in which an input port or output port of the dielectric strip is tapered and one end of the waveguide in the form of a rectangular horn is arranged in proximity to the tapered portion.
However, in the type of the sixth conventional construction example in which the end of the dielectric strip is tapered as described above when the dielectric strip of the NRD guide and the waveguide are connected, the length of the tapered portion needs to be longer than twice the wavelength of a high-frequency signal. This is disadvantageous in miniaturizing the millimeter wave integrated circuit.
The construction shown in FIG. 40 is advantageous in terms of miniaturization. However, in the connecting construction using the micro-strip, a transmission loss itself increases when the frequency of the high-frequency signal lies in a millimeter band at or above 30 GHz. This connecting construction is not suitable for the circuit board whose signal frequency is 30 GHz or longer.
It has been also difficult to suppress a transmission loss of a high-frequency signal to or below a specified value in any of the NRD guides according the sixth conventional construction.
It is an object of the present invention to provide an excellent NRD guide and a millimeter wave transmitting/receiving apparatus which are free from the problems residing in the prior art.
According to an aspect of the invention, a NRD guide comprises a pair of parallel plate conductors opposed to each other at a spacing equal to or shorter than half the wavelength of a high-frequency signal to be transmitted and having opposing inner surfaces whose arithmetic average roughness Ra satisfies 0.1 xcexcmxe2x89xa6Raxe2x89xa650 xcexcm, and a dielectric strip arranged between the pair of parallel plate conductors while being held in contact with the respective inner surfaces of the parallel plate conductors.
With this construction, since the parallel plate conductors are formed such that the arithmetic average roughness Ra of their inner surfaces satisfies 0.1 xcexcmxe2x89xa6Raxe2x89xa650 xcexcm, the inner surfaces have a suitable unevenness, and the dielectric strip is strongly secured to the inner surfaces by the anchor effect to exhibit an excellent durability. Further, current paths on the inner surfaces can be shortened to reduce a surface resistance, with the result that a transmission loss of the high-frequency signal can be effectively suppressed.
According to another aspect of the invention, a millimeter wave transmitting/receiving apparatus comprises: a pair of parallel plate conductors opposed to each other at a spacing equal to or shorter than half the wavelength of a high-frequency signal to be transmitted; a circulator made of two ferromagnetic plates provided between the pair of parallel plate conductors and opposed to each other in the same direction as the pair of parallel plate conductors are spaced apart; a first dielectric strip arranged between the pair of parallel plate conductors; a millimeter wave signal oscillator provided at one end of the first dielectric strip for outputting a millimeter wave signal to be transmitted; a second dielectric strip connected with the one end of the first dielectric strip and radially arranged with respect to the circulator between the pair of parallel plate conductors; a third dielectric strip radially arranged with respect to the circulator between the pair of parallel plate conductors and having a transmitting/receiving antenna at its leading end; a fourth dielectric strip radially arranged with respect to the circulator between the pair of parallel plate conductors; first, second, third and fourth mode suppressors arranged between the one end of the first dielectric strip and the millimeter wave signal oscillator and between the second, third and fourth dielectric strips and the circulator, and formed by arranging a plurality of conductive layers at specified intervals in a plane parallel to a transmission direction of a high-frequency signal inside the ends of the respective dielectric strips; and a mixer for mixing part of the millimeter wave signal outputted from the millimeter wave signal oscillator and a radio wave received by the transmitting/receiving antenna to generate an intermediate-frequency signal by coupling an intermediate position of the first dielectric strip and that of the fourth dielectric strip to each other.
With this construction, the electromagnetic waves of the LSE mode or the like which is an unnecessary mode can be effectively attenuated, and the transmission loss of the electromagnetic waves of the LSM mode or the like which is a transmission mode is reduced. Further, since part of the transmitted wave is introduced to the mixer via the circulator to a reduced degree, an excellent transmission characteristic of the millimeter wave signal is obtained and noise of the received wave is reduced to increase a detection distance in the case that this millimeter wave transmitting/receiving apparatus is applied to a millimeter wave radar or the like.
According to still another aspect of the invention, a millimeter wave transmitting/receiving apparatus comprises: a pair of parallel plate conductors opposed to each other at a spacing equal to or shorter than half the wavelength of a high-frequency signal to be transmitted; a circulator made of two ferromagnetic plates provided between the pair of parallel plate conductors and opposed to each other in the same direction as the pair of parallel plate conductors are spaced apart; a first dielectric strip radially arranged with respect to the circulator between the pair of parallel plate conductors; a millimeter wave signal oscillator provided at one end of the first dielectric strip for outputting a millimeter wave signal to be transmitted; a second dielectric strip radially arranged with respect to the circulator between the pair of parallel plate conductors and having a transmitting antenna at its leading end; a third dielectric strip radially arranged with respect to the circulator between the pair of parallel plate conductors; first, second, third and fourth mode suppressors arranged between one end of the first dielectric strip and the millimeter wave signal oscillator and between the first, second and third dielectric strips and the circulator, and formed by arranging a plurality of conductive layers at specified intervals in a plane parallel to a transmission direction of a high-frequency signal inside the ends of the respective dielectric strips; a fourth dielectric strip having one end connected with the first or second dielectric strip between the pair of parallel plate conductors for transmitting part of the millimeter wave signal outputted from the millimeter wave signal oscillator; a fifth dielectric strip arranged between the pair of parallel plate conductors and having a receiving antenna at its leading end; and a mixer for mixing part of the millimeter wave signal outputted from the millimeter wave signal oscillator and a radio wave received by the receiving antenna to generate an intermediate-frequency signal by coupling an intermediate position of the fourth dielectric strip and that of the fifth dielectric strip to each other.
With this construction, the electromagnetic waves of the LSE mode or the like which is an unnecessary mode can be effectively attenuated, and the transmission loss of the electromagnetic waves of the LSM mode or the like is reduced. Further, the millimeter wave signal received by the transmitting antenna is not introduced to the millimeter wave signal oscillator. Accordingly, an excellent transmission characteristic of the millimeter wave signal is obtained and noise caused by oscillation is reduced to increase a detection distance in the case that this millimeter wave transmitting/receiving apparatus is applied to a millimeter wave radar module.
According to yet still another aspect of the invention, a millimeter wave transmitting/receiving apparatus comprises: a pair of parallel plate conductors opposed to each other at a spacing equal to or shorter than half the wavelength of a millimeter wave signal to be transmitted; a circulator made of two ferromagnetic plates provided between the pair of parallel plate conductors and opposed to each other in the same direction as the pair of parallel plate conductors being spaced apart; a first dielectric strip radially arranged with respect to the circulator between the pair of parallel plate conductors; a millimeter wave signal oscillator provided at one end of the second dielectric strip for outputting the millimeter wave signal to be transmitted; a second dielectric strip radially arranged with respect to the circulator between the pair of parallel plate conductors, and having a transmitting/receiving antenna at it leading end; a third dielectric strip radially arranged with respect to the circulator between the pair of parallel plate conductors; a fourth dielectric strip radially arranged with respect to the circulator between the pair of parallel plate conductors, and having one end connected with the first dielectric strip; first, second and third mode suppressors arranged between the first, second and third dielectric strips and the circulator for suppressing electromagnetic waves of unnecessary modes; first, second and third impedance matching members arranged at the end faces of the first, second and third mode suppressors toward the circulator and having a relative dielectric constant different from that of the first, second and third dielectric strips; and a mixer for mixing part of the millimeter wave signal outputted from the millimeter wave signal oscillator and having transmitted in the fourth dielectric strip and a radio wave received by the transmitting/receiving antenna to generate an intermediate-frequency signal and transmitted in the third dielectric strip by coupling an intermediate position of the third dielectric strip and that of the fourth dielectric strip to each other.
With this construction, the transmission loss and isolation characteristic of the millimeter wave signal in a high-frequency band having a wide range are further improved, with the result that a detection distance can be increased in the case that this millimeter wave transmitting/receiving apparatus is applied to a millimeter wave radar or the like.
According to further aspect of the invention, a millimeter wave transmitting/receiving apparatus comprises: a pair of parallel plate conductors opposed to each other at a spacing equal to or shorter than half the wavelength of a millimeter wave signal to be transmitted; a circulator made of two ferromagnetic plates provided between the pair of parallel plate conductors and opposed to each other in the same direction as the pair of parallel plate conductors are spaced apart; a first dielectric strip radially arranged with respect to the circulator between the pair of parallel plate conductors; a millimeter wave signal oscillator provided at one end of the first dielectric strip for outputting the millimeter wave signal to be transmitted; a second dielectric strip radially arranged with respect to the circulator between the pair of parallel plate conductors and having a transmitting antenna at its leading end; a third dielectric strip radially arranged with respect to the circulator between the pair of parallel plate conductors; first, second and third mode suppressors arranged between the first, second, and third dielectric strips and the circulator for suppressing electromagnetic waves of unnecessary modes; first, second and third impedance matching members arranged at the end faces of the first, second and third mode suppressors toward the circulator and having a relative dielectric constant different from that of the second, third and fourth dielectric strips; a fourth dielectric strip having one end connected with the first dielectric strip between the pair of parallel plate conductors for transmitting part of the millimeter wave signal outputted from the millimeter wave signal oscillator; a fifth dielectric strip arranged between the pair of parallel plate conductors and having a receiving antenna at its leading end; and a mixer for mixing part of the millimeter wave signal outputted from the millimeter wave signal oscillator -and a radio wave received by the receiving antenna to generate an intermediate-frequency signal by coupling an intermediate position of the fourth dielectric strip and that of the fifth dielectric strip to each other.
With this construction, the transmission loss and isolation characteristic of the millimeter-wave signal in a high-frequency band having a wide range are further improved. Further, the millimeter wave signal to be transmitted is not introduced to the mixer via the circulator. Accordingly, noise of the received signal is reduced to increase a detection distance, and an excellent transmission characteristic of the millimeter wave signal further increases the detection distance of a millimeter wave radar in the case that this millimeter wave transmitting/receiving apparatus is applied to a millimeter wave radar module.
According to still further aspect of the invention, a millimeter wave transmitting/receiving apparatus comprises: a pair of parallel plate conductors opposed to each other at a spacing equal to or shorter than half the wavelength of a millimeter wave signal to be transmitted; a circulator made of two ferromagnetic plates provided between the pair of parallel plate conductors and opposed to each other in the same direction as the pair of parallel plate conductors being spaced apart; a first dielectric strip radially arranged with respect to the circulator between the pair of parallel plate conductors; a millimeter wave signal oscillator provided at one end of the first dielectric strip for outputting the millimeter wave signal to be transmitted; a second dielectric strip radially arranged with respect to the circulator between the pair of parallel plate conductors; a third dielectric strip radially arranged with respect to the circulator between the pair of parallel plate conductors; a fourth dielectric strip radially arranged with respect to the circulator between the pair of parallel plate conductors; a metallic waveguide having an open termination at one end connected with an opening formed in at least one of the pair of parallel plate conductors in a position corresponding to where the electric field of a standing wave of LSM mode transmitting in the third dielectric strip is at maximum while having an open termination at the other end provided with a transmitting/receiving antenna; a mixer for mixing part of the millimeter wave signal from the millimeter wave signal oscillator having transmitted in the fourth dielectric strip and a radio wave having transmitted in the third dielectric strip and received by the transmitting/receiving antenna to generate an intermediate-frequency signal by coupling an intermediate position of the third dielectric strip and that of the fourth dielectric strip to each other.
With this construction, an excellent transmission characteristic of the millimeter wave signal can be obtained, which in turn increases a detection distance of a millimeter wave radar.
According to yet further aspect of the invention, a millimeter wave transmitting/receiving apparatus, comprising: a pair of parallel plate conductors opposed to each other at a spacing equal to or shorter than half the wavelength of a millimeter wave signal to be transmitted; a circulator made of two ferromagnetic plates provided between the pair of parallel plate conductors and opposed to each other in the same direction as the pair of parallel plate conductors being spaced apart; a first dielectric strip radially arranged with respect to the circulator between the pair of parallel plate conductors; a millimeter wave signal oscillator provided at one end of the second dielectric strip for outputting the millimeter wave signal to be transmitted; a second dielectric strip radially arranged with respect to the circulator between the pair of parallel plate conductors; a third dielectric strip radially arranged with respect to the circulator between the pair of parallel plate conductors; a fourth dielectric strip having one end connected with the first dielectric strip between the pair of parallel plate conductors for transmitting part of the millimeter wave signal outputted from the millimeter wave signal oscillator; a fifth dielectric strip arranged between the pair of parallel plate conductors; a first metallic waveguide having an open termination at one end connected with an opening formed in at least one of the pair of parallel plate conductors in a position corresponding to where the electric field of a standing wave of LSM mode transmitting in the second dielectric strip is at maximum while having an open termination at the other end provided with a transmitting antenna; a second metallic waveguide having an open termination at one end connected with an opening formed in at least one of the pair of parallel plate conductors in a position corresponding to where the electric field of a standing wave of LSM mode transmitting in the fifth dielectric strip is at maximum while having an open termination at the other end provided with a receiving antenna; and a mixer for mixing part of the millimeter wave signal outputted from the millimeter wave signal oscillator and a radio wave received by the receiving antenna to generate an intermediate-frequency signal by coupling an intermediate position of the fourth dielectric strip and that of the fifth dielectric strip to each other.
With this construction, the millimeter wave signal to be transmitted is not introduced to the mixer via the circulator. As a result, noise of the received signal is reduced to increase a detection distance, and an excellent transmission characteristic of the millimeter wave signal further increases the detection distance of a millimeter wave.
These and other objects, features and advantages of the present invention will become more apparent upon a reading of the following detailed description and accompanying drawings.